1. Field of the Invention
The invention relates to a method for preparing a phosphorus-containing benzoxazine resin, and particularly, the invention relates to a method for preparing a benzoxazine resin with high degree of purity and high yield from phosphorus-containing diamine.
2. Description of the Prior Art
Phenolic novolac resin is the thermosetting resin usually used nowadays, and it is obtained by the condensation polymerization of phenol monomer and formaldehyde monomer. The benzoxazine resin developed in the present days belongs to a type of phenolic novolac resin and the monomer of the bexzoxazine resin decyclizes and hardens after heating. Compared to the traditional phenolic novolac resin, the benzoxazine resin has the advantages of high glass transition temperature, high modulus, low hygroscopicity, high char yield, no catalyst needed, no by-product, and small variation of volume during hardening.
However, the compositions of phenolic novolac resin are carbon, hydrogen, and oxygen, and the compositions have disadvantage of ignition for the application. With the development of the electronic industry, the product tends to miniaturization. Therefore, the traditional pin through hole (PTH) technology is replaced by the surface mount technology (SMT), such as Ball Grid Array (BGA), flip chip package, and chip size package (CSP), so as to promote the printed circuit board toward high density and multi-layer. Besides, the demands of the resistance against high temperature and ignition on the materials of the semiconductor industry rise, such as the standard UL-94 V-0 of the electronic material, so that the electronic materials tend to be difficult to ignite.
The ignition resistant benzoxazine resin on the market needs carbon fibers added in the resin to increase the resistance against ignition. However, the benzoxazine resin is still not efficient for resisting against ignition, so that the igniting problem of the benzoxazine resin becomes an important issue for the electronic industry. Savants from all circles keep focusing on the resistance against ignition of the polymer material, and a contention that alkyne, deoxybenzin, or phosphorus-containing material can increase the resistance against ignition of the polymer material has been brought up.
It is obvious that most of bifunctional benzoxazine resin is made through bisphenol, single-functional amine monomer, and formaldehyde. Therefore, the elements having the flame retardancy can be added in the bisphenol or the single-functional amine, such as bisphenol monomer having phosphoryl bond or the derivatives of DOPO to achieve the purpose of increasing the resistance against ignition of the benzoxazine resin.
There are few documents describing the bifunctional benzoxazine monomer whose matrix is diamine. The reason is that the gel phenomenon occurs when the bifunctional benzoxazine monomer is synthesized from diamine through the traditional path. When the diamine reacts with the formaldehyde and the phenol, the diamine and the formaldehyde react to obtain an intermediate of triazine which is insolvable, so that the synthesis of the benzoxazine monomer whose matrix is diamine can not proceed successfully.